There is a color developing phenomenon created by periodic structures having a wavelength comparable to or smaller than the wavelength of light. In this color developing phenomenon, colors are developed by exclusively reflecting or transmitting light having a specific wavelength, through diffraction, interference and diffusion ascribed to the periodic structures, although the substances in the structures have no light absorbability. This color developing phenomenon is different from the one created by pigments, through electron transition ascribed to light absorption. Hereinafter, in the present specification, this color developing phenomenon using periodic structures is referred to as structural color development.
When periodic structures are formed, for example, of inorganic dielectric materials that are not deteriorated by ultraviolet light, the structural color development will not be impaired, as long as the structures are retained, even if the structures are left exposed to ultraviolet light.
Further, structural color development through diffraction and interference is characterized in that the recognized wavelength of light changes, depending on the observation angle, and therefore expressions with high designability can be accomplished.
As a color developing member for such structural color development, a color developing structure utilizing multilayer film interference is being proposed (Patent Literature 1). This color developing structure includes a multilayer structure made of polymer materials having different refractive indices.
The color developing structure proposed in Patent Literature 1 has a multilayer structure made of polymer materials, and therefore there is only a small difference in refractive index of the materials forming the adjoining layers. Therefore, it is necessary to laminate a number of layers to accomplish intense reflection and thus the production cost increases. In addition, in the proposed structure, the influence of the multilayer film interference becomes dominant, and the color change depending on the observation angle becomes abrupt. Therefore, it is difficult to express specific colors.
As measures against these problems, another type of color developing member is being proposed (Patent Literature 2). This color developing member provides intense reflection, and exhibits a moderate color change depending on the observation angle, as do Morpho butterflies inhabiting a natural environment.